Turkish police have fired tear gas in Istanbul to disperse several hundred people protesting against the police crackdown on last month's antigovernment demonstrations.

Police blocked at least 500 protesters in a busy street near Istanbul's Taksim Square from marching in support of a teenage boy who is said to be in a coma after being hit in the head by a tear-gas canister during the unrest.

An initially small protest against the planned redevelopment of the city's Gezi Park snowballed into nationwide demonstrations last month against Prime Minister Recep Tayyip Erdogan, accused by his critics of becoming increasingly authoritarian.

Five people died and thousands were injured in the unrest, which posed the biggest threat to Erdogan's decade-long rule.

Some isolated demonstrations have persisted in Istanbul and the capital, Ankara.